The present invention relates generally to methods of surface treating a metal article, such as chemical-mechanical polishing (CMP) metal surfaces. The present invention has particular applicability in CMP non-magnetic substrates for use in manufacturing high areal density magnetic recording media exhibiting low noise and high coercivity.
Throughout various industries, metals are processed chemically and/or mechanically thereby altering the surface properties and rendering them less amenable to subsequent surface processing tailored for the chemical and/or physical properties of the bulk metal, such as grinding or CMP. Such alteration results in decreased yield, reduced production throughput and product inferiority.
Various metal platings, such as nickel (Ni) platings or deposits, enjoy technological applicability in various industries, such as the electronic, oil and gas, aerospace, machinery, automobile and magnetic recording media industries. For example, electroless Ni is employed in the metal finishing industry for various metal substrates, including steel, copper, aluminum and alloys thereof Conventional electrolessly deposited Nixe2x80x94P platings exhibit desirable physical and chemical properties, such as hardness, lubricity, appearance, and corrosion resistance. An amorphous Nixe2x80x94P plating is conventionally applied to a non-magnetic substrate, such as aluminum (Al) or an Al-alloy substrate in manufacturing magnetic recording media.
In operation, a magnetic disk is normally driven by the contact start-stop (CSS) method, wherein the head begins to slide against the surface of the disk as the disk begins to rotate and, upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk during reading and recording operations, the transducing head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head begins to slide against the surface of the disk again and eventually stops in contact with and pressing against the disk. Thus, each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too smooth, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as xe2x80x9chead crash.xe2x80x9d Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a non-magnetic substrate with a hard metal plating thereon, e.g.; Nixe2x80x94P, polishing, as by CMP, to obtain a smooth surface and then roughening a dedicated landing zone to reduce the head/disk friction by techniques generally referred to as xe2x80x9ctexturing.xe2x80x9d Conventional texturing involves mechanical polishing or laser texturing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers.
It is recognized, however, that electroless metal plating, such as electroless Nixe2x80x94P plating of a non-magnetic substrate, even subsequent to smoothening, does not achieve a coating exhibiting a desired degree of surface smoothness, particularly the degree of smoothness necessary to satisfy the high areal recording density objectives of current magnetic recording media. For example, ridgeline defects cause media glide and certify test failure. Ridgeline defects are caused by deformation of the Nixe2x80x94P layer prior to polishing. Subsequent to polishing, surface deformation is smoothened and may pass inspection. However, upon sputter depositing subsequent layers thereon, the pre-deformed area becomes a ridge upon stress relieving at elevated temperatures. Attempts to rebake and repolish have been unsuccessful.
Conventional techniques for treating various metal surfaces, such as Al, Ni and Nixe2x80x94P, include CMP for smoothening. In conventional CMP techniques, a wafer carrier assembly is rotated in contact with a polishing pad in a CMP apparatus. The polishing pad is mounted on a rotating turntable or platen, or moving above a stationary polishing table, driven by an external driving force. The wafers are typically mounted on a carrier or polishing head which provides a controllable pressure urging the wafers against the rotating polishing pad. Thus, the CMP apparatus effects polishing or rubbing movement between the surface of each thin semiconductor wafer and the polishing pad while dispersing a polishing slurry, typically containing abrasive particles in a reactive solution typically comprising an oxidizer, to effect both chemical activity and mechanical activity while applying a force between the wafer and a polishing pad. In fixed abrasive articles, the abrasive particles are formed as columnar posts on a backing sheet and CMP is conducted using an abrasive-free chemical agent.
It is, however, extremely difficult to smoothen a hardened non-magnetic substrate without encountering severe surface defects, such as surface roughness, scratches and pitting. These surface defects are virtually impossible to recover without the expenditure of an inordinate, prohibitive amount of polishing time. Conventional smoothening methodology, therefore, cannot provide a non-magnetic substrate with a hardened surface having an average surface roughness (Ra) less than 4 xc3x85 to 5 xc3x85.
There exists a need for methodology enabling surface treatment, such as CMP, of metal surfaces with reduced defects and enhanced production throughput. There exists a particular need for methodology enabling the manufacture of magnetic recording media comprising a non-magnetic substrate having a smoothened surface with an Ra less than 4 xc3x85.
An advantage of the present invention is an efficient method for surface treating a metal with reduced surface defects.
Another advantage of the present invention is a method of manufacturing a magnetic recording media comprising CMP the surface of a hardened non-magnetic substrate with reduced surface defects and enhanced production throughput.
According to the present invention, the foregoing and other advantages achieved by a method of manufacturing a magnetic recording medium, the method comprising: treating a surface of a non-magnetic substrate having an oxide layer thereon to substantially remove the oxide layer; and chemical-mechanical polishing (CMP) the treated surface.
Embodiments of the present invention comprise electrolessly depositing a Ni or Nixe2x80x94P layer on a non-magnetic substrate, baking in air to form a hardened oxide film having a thickness of about 80 xc3x85 or greater, soaking in an acid bath, e.g., a bath comprising sulfuric acid and phosphoric acid in deionized water, and subsequently conducting CMP to provide a smoothened surface with a Ra of about 2 xc3x85 to about 3 xc3x85.
Another aspect of the present invention is a method of surface treating an article having a metal surface, the method comprising: processing the article such that a surface layer is formed on the surface exhibiting properties different from those of the underlying metal; chemically removing the surface layer and/or chemically modifying the surface such that the surface defects upon subsequent surface treatment are reduced; and surface treating the article.